A single-medium metasurface with geometrically compensated phase and its preparation method

Abstract

The present invention relates to the field of optical element technology, and specifically to a single-medium metasurface with geometrically compensated phase and a preparation method thereof. The single-medium metasurface includes at least one periodically arranged metasurface unit; the metasurface unit includes a substrate, the substrate has two substrate surfaces, and the two adjacent substrate surfaces have a height difference; there are two groups of superunits, which are periodically arranged on the substrate, and each group of superunits is arranged on a corresponding substrate surface; each group of superunits is formed by a periodic arrangement of multiple cellular structures. The present invention utilizes superunits periodically arranged on the substrate to generate a specific phase distribution, and utilizes the substrate surface with a height difference to provide additional phase compensation, thereby realizing a single-medium metasurface covering a phase distribution of 0 to 2π, reducing the processing difficulty and improving the processing accuracy on the basis of reducing the aspect ratio of the cellular structure.

Description

Technical Field

[0001] The present invention relates to the technical field of optical elements, and in particular to a single-medium metasurface for geometrically compensating phase and a preparation method thereof. Background Art

[0002] Precise beam control is crucial in modern optical applications. Traditional beam control technologies rely primarily on mechanical beam controllers, liquid crystal spatial light modulators, or traditional metasurfaces. While these technologies can meet these requirements in some situations, they all have limitations.

[0003] Macroscopic mechanical beam deflectors and liquid crystal spatial light modulators suffer from large size, slow response, limited precision, and high cost, making them difficult to meet the miniaturization, integration, and high-performance demands of modern optical systems. Metasurfaces, a new type of two-dimensional subwavelength structure, can precisely control the amplitude, phase, and polarization of light waves. They offer advantages such as small size, light weight, and ease of integration, and are becoming a research hotspot in beam deflection technology.

[0004] Liquid crystal integrated metasurfaces, such as those in CN117724279A and CN118672005A, achieve flexible light beam deflection through dynamic control of liquid crystal materials. However, their multi-layered structure, complex processing, and poor material compatibility make it difficult to achieve low-cost, large-scale production while maintaining high performance. On-chip integrated beam deflectors based on phase-change materials and metasurfaces, due to their complex structure, the involvement of multiple materials and processes, and high manufacturing costs, limit their applicability in different scenarios.

[0005] Conventional dielectric metasurface beam deflectors, such as those described in CN113885115B and CN119644608A, typically achieve phase control through geometric parameters of the cellular structure, such as size and shape. To cover the phase range of 0 to 2π, the cellular structure must have a large aspect ratio, which makes fabrication difficult. This is especially true for materials with high refractive indexes, where excessive aspect ratios can lead to structural instability and difficulty in ensuring fabrication accuracy. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention provides a single-medium metasurface with geometrically compensated phase and a preparation method thereof.

[0007] To achieve the above objectives, the technical solutions of the present invention are as follows.

[0008] A first aspect of the present invention provides a single-medium metasurface with geometrically compensated phase, comprising at least one periodically arranged metasurface unit; the metasurface unit comprises: a substrate having two substrate surfaces, with a height difference between two adjacent substrate surfaces; two groups of superunits periodically arranged on the substrate, with each group of superunits arranged on a corresponding substrate surface; each group of superunits is formed by a periodic arrangement of multiple cellular structures; along the periodic arrangement direction, the width of the cellular structure of each group of superunits gradually changes, so that the single-medium metasurface covers a phase range of 0 to 2π.

[0009] The present invention mainly uses super units periodically arranged on a substrate to generate a specific phase distribution with a net phase change of π, and the substrate surface with a height difference compensates for the additional π phase, thereby realizing a single-medium metasurface covering a phase distribution of 0 to 2π.

[0010] The direction of a transmitted light beam passing through the single-medium metasurface of the present invention will be deflected. The deflection angle is determined by the phase gradient of the metacell. The substrate surface with a height difference provides additional π phase compensation, thereby reducing the aspect ratio of the cellular structure. In addition, the single-medium metasurface proposed by the present invention only requires one material, reducing the difficulty of processing.

[0011] Preferably, the widths of two adjacent cellular structures are different; and the aspect ratio of the cellular structure is ≤ 4. At the same deflection angle, compared to the maximum aspect ratio of the cellular structure of a conventional metasurface beam deflector, the maximum aspect ratio of the cellular structure of the present invention is relatively lower, and the maximum aspect ratio is ≤ 4.

[0012] Preferably, along the periodic arrangement direction, the width of the cellular structure of each group of the super units gradually changes from 125 nm to 185 nm, so that the net phase change of each group of the super units is π.

[0013] Preferably, along the periodic arrangement direction, the width of the cellular structure of each group of the super units gradually changes from 125 nm to 185 nm, so that each group of the super units covers a phase range of π / 2 to 3π / 2.

[0014] Along the periodic arrangement direction, the width of the cellular structure of the traditional metasurface design gradually changes from 0 to 430nm to completely cover the phase range of 0 to 2π. However, the traditional metasurface has a large depth-to-width ratio of the cellular structure, which makes processing difficult. Especially in high-refractive index materials, too large a depth-to-width ratio will lead to structural instability and difficulty in ensuring processing accuracy. Therefore, in order to improve the ultra-depth-to-width ratio defect of the traditional metasurface design, the width of the cellular structure of the present invention uses a width range of 125nm to 185nm, so that each group of super units achieves π / 2 to 3π / 2 phase coverage, that is, the net phase change is π, and the substrate surfaces with different height differences provide additional π phase compensation, thereby significantly reducing the depth-to-width ratio of the cellular structure.

[0015] The present invention precisely controls the width variation range of the cellular structure of each group of super units to form a specific phase distribution and cover the phase range of π / 2 to 3π / 2. At the same time, additional π phase compensation is provided through substrate surfaces with different height differences, thereby achieving periodic modulation of the phase from 0 to 2π on a subwavelength scale, thereby controlling the wavefront of the transmitted light beam and realizing modulation of the deflection direction of the transmitted light beam.

[0016] Preferably, each group of super units has 4 to 12 cellular structures.

[0017] Preferably, the height difference between two adjacent substrate surfaces is 0.2 μm to 3 μm.

[0018] The relationship between the height difference between two adjacent substrate surfaces and the phase compensation is:

[0019] ;

[0020] in, d represents the height difference between two adjacent substrate surfaces; λ represents the wavelength of the incident light; n represents the refractive index of the substrate material, k Represents a non-zero integer.

[0021] In the present invention, the height difference between two adjacent substrate surfaces is set to d ; According to the actual simulation results, d =0.2μm or 0.6μm can produce better deflection effect. Considering that the aspect ratio cannot be too large in actual processing, the embodiment takes d =0.6μm.

[0022] Preferably, the substrate and the super unit are both made of transparent dielectric materials; and each of the cellular structures is a dielectric nanocolumn.

[0023] In this invention, the substrate and the metacell are made of the same material, making it applicable to any transparent dielectric material. This single-medium metasurface, fabricated from a single transparent dielectric material, boasts a low aspect ratio, a highly compatible fabrication process, and is applicable to any transparent dielectric material. It holds broad application prospects in fields such as lidar and optical communications.

[0024] Preferably, in each group of the super units, the center distance between two adjacent cellular structures is 300 nm to 700 nm; and the height of each cellular structure is 300 nm to 700 nm.

[0025] A second aspect of the present invention provides a method for preparing a single-medium metasurface with geometrically compensated phase, comprising the following steps:

[0026] According to the phase gradient formula, a phase gradient data set at different deflection angles is obtained; according to the phase gradient data set at different deflection angles, the width of the cellular structure of a group of super units at different positions is substituted into the relationship model between the width and phase of the cellular structure to obtain the width of the cellular structure of each group of super units, so that the net phase change of each group of super units is π; the height difference of the substrate surfaces corresponding to adjacent super units is adjusted to perform π phase compensation, so that the single-medium metasurface covers a phase range of 0 to 2π; according to the obtained phase gradient data set at different deflection angles, the width of the cellular structure of a group of super units at different positions, and the height difference of the substrate surfaces corresponding to adjacent super units, the single-medium metasurface with geometrically compensated phase is prepared using a semiconductor micro-nano processing method.

[0027] The preparation method of the present invention first determines the optical effect, such as the deflection angle of the light beam, and then designs the structure of the single-medium metasurface. By selecting a transparent dielectric material with good optical transparency and an appropriate refractive index range, the metasurface unit of the transparent dielectric material is adjusted according to the design goal to achieve the desired phase distribution.

[0028] The semiconductor micro-nanofabrication methods described in the present invention include focused ion etching, electron beam etching, and photolithography. The semiconductor micro-nanofabrication methods described in the present invention sequentially process substrate surfaces of varying height differences and supercells located on the corresponding substrate surfaces on a transparent substrate, thereby obtaining a single-medium metasurface with a phase distribution covering 0 to 2π.

[0029] Preferably, the method for preparing the geometrically compensated phase single-medium metasurface using semiconductor micro-nano processing methods is as follows:

[0030] A certain thickness of photoresist is uniformly coated on the cleaned substrate; an exposure system is used to expose the photoresist according to a designed pattern of the substrate, and the photoresist in the exposed area is modified; the exposed substrate is immersed in an organic developer for development and deep etching, and a substrate with a height difference is obtained on the substrate surface; a certain thickness of photoresist is then uniformly coated on the substrate; an exposure system is used to expose the photoresist on the substrate according to a designed pattern of a super unit, and the photoresist in the exposed area is modified; the exposed substrate is immersed in an organic developer for development and dry etching, and a super unit is obtained on the substrate surface, forming a single-medium metasurface that covers a phase distribution of 0 to 2π.

[0031] Specifically, the substrate may be SiO2, TiO2 or other substrates.

[0032] The single-medium metasurface of the present invention is obtained by micro-nanofabrication on a substrate. The substrate serves as the base material. During the fabrication process, a base with height differences and metaunits periodically arranged on the base are formed, resulting in a single-medium metasurface with a phase distribution covering 0 to 2π. The single-medium metasurface designed and formed in the present invention has a beam deflection function and can be used as a beam deflector. Alternatively, metasurface units can be processed according to specific phase distribution requirements to form a beam focusing element, which can be used as a metalens.

[0033] Beneficial effects of the present invention:

[0034] 1. The present invention mainly utilizes super units periodically arranged on a substrate to generate a specific phase distribution, and utilizes a substrate surface with a height difference to provide additional phase compensation and support the cellular structure, thereby realizing a single-medium metasurface covering a phase distribution of 0 to 2π. On the basis of reducing the aspect ratio of the cellular structure, the processing difficulty is reduced and the processing accuracy is improved.

[0035] 2. The single-medium metasurface of this invention enables precise control of the deflection direction of a transmitted light beam. It features a simple structure, a wide range of materials, and excellent compatibility with various work platforms. This invention overcomes the limitations of conventional beam controllers, such as bulk, low precision, and high cost, as well as the large depth-to-width ratio and difficult processing of existing metasurface devices. It addresses the beam control needs of applications such as lidar and optical communications. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 Schematic diagrams of the metasurface unit structure in an embodiment of the present invention. (a) is a side view of the metasurface unit; (b) is a schematic diagram of the structure of a single cell and substrate; (c) is a schematic diagram of the three-dimensional structure of the metasurface unit.

[0037] Figure 2: is a curve showing the relationship between the width of the cell structure and the phase and transmittance in an embodiment of the present invention. D represents the width of the cell structure.

[0038] Figure 3 Schematic diagram of the structure and simulation results of a traditional metasurface beam deflector with a deflection angle of 6.14°. (a) is a schematic diagram of the structure of a traditional metasurface beam deflector with a deflection angle of 6.14°; (b) is a schematic diagram of the field intensity distribution simulation results of a traditional metasurface beam deflector with a deflection angle of 6.14°; (c) is a schematic diagram of the output phase distribution simulation results of a traditional metasurface beam deflector with a deflection angle of 6.14°.

[0039] Figure 4 Schematic diagram of the simulation results of a metasurface beam deflector with a deflection angle of 6.14° designed in an embodiment of the present invention. (a) is a schematic diagram of the simulation results of the field intensity distribution of a metasurface beam deflector with a deflection angle of 6.14° designed in an embodiment of the present invention; (b) is a schematic diagram of the simulation results of the output phase distribution of a metasurface beam deflector with a deflection angle of 6.14° designed in an embodiment of the present invention.

[0040] Figure 5 Schematic diagram of the simulation results of a metasurface beam deflector with a deflection angle of 4.60° designed in an embodiment of the present invention. (a) is a schematic diagram of the simulation results of the field intensity distribution of a metasurface beam deflector with a deflection angle of 4.60° designed in an embodiment of the present invention; (b) is a schematic diagram of the simulation results of the output phase distribution of a metasurface beam deflector with a deflection angle of 4.60° designed in an embodiment of the present invention. DETAILED DESCRIPTION

[0041] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0042] Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making any creative work shall fall within the scope of protection of the present invention.

[0043] The present invention proposes a single-medium metasurface with geometrically compensated phase, which is formed by specially designed metasurface units. The single-medium metasurface is processed from a single transparent medium material. A certain phase gradient is generated through a geometrically compensated subwavelength structure and covers a phase range of 0 to 2π, so as to control the wavefront of the transmitted light beam and realize the modulation of the deflection direction of the transmitted light beam.

[0044] The working process of the single-medium metasurface of the present invention is as follows: when a transmitted light beam incident perpendicularly to the single-medium metasurface passes through the single-medium metasurface, the metacell modulates the phase of the transmitted light beam. The modulation effect depends on the specific phase distribution of the metacell producing a net phase change of π. The substrate surface with a height difference is used to compensate for the phase difference of the metacell, thereby utilizing the single-medium metasurface with a small aspect ratio to cover the phase range of 0 to 2π, thereby achieving precise control of the wavefront of the transmitted light beam.

[0045] Specifically, the single-medium metasurface includes a substrate with a relatively small depth-to-width ratio, which is used to support the superunit and compensate the phase; the superunit is composed of a periodically arranged cellular structure with a specific size and height, which is used to generate a specific phase distribution with a net phase change of π, thereby realizing wavefront control of the transmitted light beam.

[0046] The single-medium metasurface of the present invention is primarily used to manipulate the wavefront of a parallel light beam of a specific wavelength, thereby changing the beam's propagation direction. This invention utilizes a single-medium metasurface formed from a single transparent dielectric material, replacing traditional multi-material metasurfaces. The deflection angle of the transmitted light beam is determined by the phase distribution of the metacells. By varying the arrangement of the cellular structure, different optical properties can be achieved.

[0047] In summary, the single-medium metasurface of the present invention is made of a single transparent dielectric material. At the same time, the wavefront of the transmitted light beam is determined by the phase distribution of the metacells periodically arranged on the substrate. The substrate with a height difference provides additional phase compensation, thereby reducing the aspect ratio of the cellular structure and reducing the processing difficulty.

[0048] The technical solution of the present invention is further described below through specific embodiments.

[0049] In the following examples, the methods described are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0050] Example 1

[0051] like Figure 1 As shown, a single-medium metasurface with geometrically compensated phase includes at least one periodically arranged metasurface unit; the metasurface unit includes a substrate and a superunit; the substrate has two substrate surfaces, and the two adjacent substrate surfaces have a height difference; there are two groups of superunits, which are periodically arranged on the substrate, and each group of superunits is arranged on a corresponding substrate surface; each group of superunits is formed by a periodic arrangement of multiple cellular structures; along the periodic arrangement direction, the width of the cellular structure of each group of the superunits gradually changes, so that the single-medium metasurface covers a phase range of 0 to 2π.

[0052] The embodiment of the present invention mainly uses a substrate with a height difference on the surface as the first-level structure, and a super unit periodically arranged on the substrate as the second-level structure. By using the super units periodically arranged on the substrate to generate a specific phase distribution with a net phase change of π, and the substrate surface with a height difference to compensate for the additional π phase, a single-medium metasurface covering a phase distribution of 0 to 2π is realized. The substrate and the super unit in the embodiment of the present invention are made of the same material, and any transparent medium material can be selected. The direction of the transmitted light beam passing through the single-medium metasurface of the embodiment of the present invention will be deflected, and the deflection angle is determined by the phase gradient of the super unit. The substrate surface with a height difference provides additional π phase compensation, thereby reducing the aspect ratio of the cellular structure. In addition, the single-medium metasurface proposed in the embodiment of the present invention only requires one material, reducing the difficulty of processing.

[0053] Based on the above embodiment, the widths of two adjacent cellular structures are different, and the aspect ratio of the cellular structure is ≤ 4. At the same deflection angle, compared to the maximum aspect ratio of the cellular structure of a conventional metasurface beam deflector, the maximum aspect ratio of the cellular structure of the metasurface beam deflector in the embodiment of the present invention is relatively lower, and the maximum aspect ratio is ≤ 4.

[0054] Based on the above embodiment, along the periodic arrangement direction, the width of the cellular structure of each group of supercells gradually varies from 125 nm to 185 nm, such that the net phase variation of each group of supercells is π. Specifically, along the periodic arrangement direction, the width of the cellular structure of each group of supercells gradually varies from 125 nm to 185 nm, such that each group of supercells covers a phase range of π / 2 to 3π / 2.

[0055] like Figure 1 , each super unit has multiple sub-wavelength cellular structures, and the center distance between adjacent cellular structures is a unit period, which is recorded as P ; The height of a cell structure is recorded as H , with the width of a cell structure as D ,but P =300nm~700nm, H =300nm~700nm.

[0056] Each super unit has 4 to 12 cell structures. The height difference between the two base surfaces corresponding to the two adjacent super units is d , which can be discretely valued to provide a phase compensation of π. The height difference between two adjacent substrate surfaces is 0.2μm to 3μm. For example, d The value of can be 0.2μm, 0.6μm, 1μm, 1.4μm,…, 3μm.

[0057] The relationship between the height difference between two adjacent substrate surfaces and phase compensation is:

[0058] ;

[0059] in, d Represents the height difference between two adjacent substrate surfaces; λ represents the wavelength of the incident light; n represents the refractive index of the substrate material, k Represents a non-zero integer.

[0060] In the present invention, the width of the cell structure of each super unit is set to d ; According to the actual simulation results, d =0.2μm or 0.6μm can produce better deflection effect. Considering that the aspect ratio cannot be too large in actual processing, the embodiment takes d =0.6μm.

[0061] In the embodiment of the present invention, the width of the cellular structure determines the phase delay of the transmitted light, and different phase delays are achieved by adjusting the width of the sub-wavelength cellular structure at different positions. The finite difference time domain algorithm is used to perform numerical simulation of the metasurface cellular structure. At a wavelength of 642nm, by adjusting the width of the sub-wavelength cellular structure at different positions from 125nm to 185nm, the phase delay can cover a phase range of π / 2 to 3π / 2, that is, the net phase change is π. The relationship between phase delay and light transmittance and the width of the cellular structure is as follows: Figure 2 shown. Figure 2 The relationship between the width and phase of the cellular structure is shown.

[0062] The phase delay of the single-medium metasurface satisfies the following phase gradient formula:

[0063] ， ;

[0064] in, Represents the phase difference between adjacent cell structures; K 0 is a constant; P Represents the unit period of the cellular structure, that is, the center distance between two adjacent cellular structures; represents the beam deflection angle, Indicates the wavelength of the working light.

[0065] The phase gradient formula above can be used to obtain the phase gradient required for different deflection angles. The width of the cell structure can be obtained by simulation scanning. D The correspondence with the phase is to select the width of the cellular structure that meets the phase requirements at different positions of the single-medium metasurface. D .

[0066] Using the corresponding relationship obtained in the previous step, a cellular structure of a specific size can be set at a specific position on the single-medium metasurface, and 4 to 12 cellular structures of appropriate sizes can be selected as a group of superunits. A group of superunits covers a phase range of π / 2 to 3π / 2. At the same time, the height difference of the substrate surface under adjacent superunits is changed to perform additional π phase compensation, so that a phase coverage of 0 to 2π can be achieved on the substrate surface by combining two superunits.

[0067] The metasurface units are repeated periodically to obtain a single-medium metasurface with a certain deflection angle at a specific wavelength.

[0068] The single-medium metasurface formed by this design has a beam-deflecting effect and can be used as a beam deflector. By varying the number of cellular structures in the metaunit and adjusting the cellular structure parameters according to the phase gradient formula, single-medium metasurface beam deflectors with different deflection angles can be designed.

[0069] An embodiment of the present invention provides a method for preparing a single-medium metasurface with geometrically compensated phase, comprising the following steps:

[0070] Step 1: According to the phase gradient formula, obtain phase gradient data sets at different deflection angles.

[0071] According to the target beam deflection angle, for example, 5°, a phase gradient data set corresponding to the target deflection angle is calculated according to the beam deflector surface phase formula.

[0072] The surface phase formula of the beam deflector is: ;in, x is the position coordinate corresponding to the center of the cell structure, λ is the wavelength of incident light, θ is the target beam deflection angle.

[0073] The calculated phase gradient data set is stored as design parameters for subsequent structural design.

[0074] Step 2: Based on the phase gradient data sets at different deflection angles, substitute the relationship model between the width and phase of the cellular structure to obtain the width of the cellular structure of a group of super units at different positions so that the net phase change of each group of super units is π.

[0075] The full name of the finite-difference time-domain method is Finite-Difference Time-Domain, or FDTD for short. D The phase response of the cell structure is obtained by D The correspondence between the width and phase of the cell structure is established, and a relationship model between the width and phase of the cell structure is established.

[0076] According to the phase gradient data set in step 1, the relationship model between the width and phase of the cellular structure is used to determine the width of the cellular structure of each group of super units at different positions to ensure that each group of super units can cover the phase range of 0 to π.

[0077] Step 3: Adjust the height difference of the substrate surface corresponding to adjacent super units to perform π phase compensation so that the single-medium metasurface covers a phase range of 0 to 2π.

[0078] According to the target phase compensation requirement, the height difference of the substrate surfaces corresponding to adjacent super units is determined. The relationship between the height difference of two adjacent substrate surfaces and the phase compensation is:

[0079] ;in, d represents the height difference between two adjacent substrate surfaces; λ represents the wavelength of the incident light; n represents the refractive index of the substrate material, k Represents a non-zero integer.

[0080] By adjusting the height difference between two adjacent substrate surfaces, additional π phase compensation is achieved, ensuring that the entire single-medium metasurface can cover a phase range of 0 to 2π. Phase continuity is ensured by optimizing the height difference between two adjacent substrate surfaces.

[0081] Step 4: Based on the acquired phase gradient data sets at different deflection angles, the widths of the cellular structures of a group of superunits at different positions, and the height differences of the substrate surfaces corresponding to adjacent superunits, a semiconductor micro-nano processing method is used to prepare the single-medium metasurface with the geometrically compensated phase.

[0082] The semiconductor micro-nanofabrication methods include focused ion etching, electron beam etching, and photolithography. The semiconductor micro-nanofabrication methods described in the embodiments of the present invention sequentially process substrate surfaces of varying height differences and supercells located on the corresponding substrate surfaces on a transparent substrate, thereby obtaining a metasurface that achieves a phase distribution covering 0 to 2π.

[0083] The following describes the specific preparation method of a single-medium metasurface by taking the photolithography method as an example.

[0084] Step 4.1: prepare a TiO2 substrate and clean the substrate to ensure that the surface is clean and has good flatness, thereby obtaining a cleaned substrate.

[0085] In step 4.2, a certain thickness of photoresist is evenly coated on the cleaned substrate; the photoresist is exposed using an exposure system according to a designed pattern of the substrate, and during the exposure process, the photoresist in the exposed area is modified; the exposed substrate is immersed in an organic developer for development and deep etching, thereby obtaining a substrate with a height difference on the substrate surface.

[0086] During the development process of the substrate sample immersed in an organic developer, the negative photoresist solidifies due to electron beam exposure and is not dissolved by the developer, while the positive photoresist degrades due to electron beam exposure and is dissolved by the developer. Deep etching uses inductively coupled etching technology to dry-etch the developed structure, forming the exposed first-level structure on the substrate.

[0087] In step 4.3, use a chemical solvent to remove the residual photoresist on the surface, and then follow the method in step 4.1 to obtain a second-level structure on the substrate surface to form a single-medium metasurface with geometric compensation phase. The specific method is as follows:

[0088] Then, a certain thickness of photoresist is evenly coated on the substrate; then, an exposure system is used to expose the photoresist on the substrate according to the designed super-unit pattern, and the photoresist in the exposed area is modified; the exposed substrate is immersed in an organic developer for development and dry etching, and a super-unit is obtained on the surface of the substrate, forming a single-medium metasurface that covers a phase distribution of 0 to 2π.

[0089] Example 2

[0090] A beam deflector composed of a single-medium metasurface, the beam deflector is composed of a super unit arrangement of 6 cell structures as a group, and the deflection angle is 6.14°, such as Figure 4 The preparation method of the single-medium metasurface is the same as that in Example 1, and both the substrate and the superunit are made of a single-medium material.

[0091] The height difference between two adjacent base surfaces of the first-level structure d Discrete changes, and d =0.2μm to provide additional π phase compensation. In the second-level structure, each superunit group contains 6 cellular structures. The parameters of the cellular structures corresponding to each superunit group are the same. A superunit group covers the phase from π / 2 to 3π / 2, and the phase changes in a gradient. The overall beam deflector can achieve a phase gradient covering 0 to 2π.

[0092] After the parallel light beam passes through the substrate of the single-medium metasurface, it is modulated by the cellular structure array of the super unit on the substrate to produce a phase gradient distribution, and the final output light beam is deflected at a specific angle. θThe deflection angle can be precisely controlled by adjusting the width and height of the cellular structure, which is proportional to the phase gradient of the single-medium metasurface.

[0093] The wavelength of a parallel light beam has a specific range. After the medium is determined, the cellular structure of the metasurface that constitutes the beam deflector is simulated and scanned to determine the parameters of the cellular structure that meet the phase and transmittance requirements.

[0094] like Figure 3 At the same deflection angle of 6.14°, the maximum aspect ratio of the cellular structure of a conventional metasurface beam deflector is 6.47. However, the maximum aspect ratio of the cellular structure of the metasurface beam deflector in the embodiment of the present invention is significantly reduced to 3.9, a reduction of 39.7%. The geometrically compensated phase-based metasurface beam deflector designed in the embodiment of the present invention has a smaller cellular structure aspect ratio while maintaining a good beam deflection effect.

[0095] Example 3

[0096] A beam deflector composed of a single-medium metasurface, the beam deflector is composed of a super unit arrangement of 8 cell structures as a group, and the deflection angle is 4.60°, such as Figure 5 The preparation method of the single-medium metasurface is the same as that in Example 1, and both the substrate and the superunit are made of a single-medium material.

[0097] The height difference between two adjacent base surfaces of the first-level structure d Discrete changes, and d =0.6μm to provide additional π phase compensation. In the second-level structure, each superunit group contains 8 cellular structures. The parameters of the cellular structures corresponding to each superunit group are the same. A superunit group covers the phase from π / 2 to 3π / 2, and the phase changes in a gradient. The overall beam deflector can achieve a phase gradient covering 0 to 2π.

[0098] When the deflection angle is also 4.60°, the maximum aspect ratio of the cellular structure of the conventional metasurface beam deflector is 8.50. However, the maximum aspect ratio of the cellular structure of the metasurface beam deflector of the embodiment of the present invention is reduced to 4.0, a reduction of 56.3%.

[0099] The above results show that the single-medium metasurface of the embodiment of the present invention is composed of any single transparent medium material, and the functional unit and the substrate are made of the same transparent medium material. According to the methods of Example 2 and Example 3, a composite structure metasurface beam deflector with a specific deflection angle is constructed. By changing the height difference between the two adjacent substrate surfaces of the first-level structure dBy providing an additional π phase, the supercell only needs to cover the π / 2 to 3π / 2 phase, and the entire metasurface can cover the 0 to 2π phase range. As a result, the aspect ratio of the metasurface's cellular structure can be significantly reduced to about 50% of the original, significantly reducing the difficulty of metasurface device processing and greatly expanding the range of metasurface device material options, accelerating the integration and practical application of metasurface technology.

[0100] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A single-medium metasurface with geometrically compensated phase, comprising at least one periodically arranged metasurface unit; the metasurface unit comprising: A substrate having two substrate surfaces, wherein two adjacent substrate surfaces have a height difference to perform π phase compensation; Super units, having two groups, and periodically arranged on the substrate, each group of super units being arranged on a corresponding substrate surface; Each group of superunits is formed by a periodically arranged plurality of cellular structures; along the periodic arrangement direction, the width of the cellular structure of each group of superunits gradually changes, so that the net phase change of each group of superunits is π, so that the single-medium metasurface covers a phase range of 0 to 2π; The widths of two adjacent cellular structures are different; and the aspect ratio of the cellular structure is ≤4.

2. The single-medium metasurface with geometrically compensated phase according to claim 1, characterized in that: Along the periodic arrangement direction, the width of the cellular structure of each group of the super units gradually changes from 125 nm to 185 nm, so that the net phase change of each group of the super units is π.

3. The single-medium metasurface with geometrically compensated phase according to claim 2, characterized in that: Along the periodic arrangement direction, the width of the cellular structure of each group of the super units gradually changes from 125 nm to 185 nm, so that each group of the super units covers a phase range of π / 2 to 3π / 2.

4. The single-medium metasurface with geometrically compensated phase according to claim 1, characterized in that: Each group of super units has 4 to 12 cell structures.

5. The single-medium metasurface with geometrically compensated phase according to claim 1, characterized in that: The height difference between two adjacent substrate surfaces is 0.2 μm to 3 μm.

6. The single-medium metasurface with geometrically compensated phase according to claim 1, characterized in that: The materials of the substrate and the super unit are both transparent dielectric materials; and each of the cellular structures is a dielectric nanocolumn.

7. The single-medium metasurface with geometrically compensated phase according to claim 1, characterized in that: In each group of the super units, the center distance between two adjacent cellular structures is 300nm to 700nm; and the height of each cellular structure is 300nm to 700nm.

8. A method for preparing the geometrically compensated phase single-medium metasurface according to claim 1, comprising the following steps: According to the phase gradient formula, phase gradient data sets at different deflection angles are obtained; Substituting the phase gradient data sets at different deflection angles into the relationship model between the width and phase of the cellular structure, the widths of the cellular structures of a group of super units at different positions are obtained, so that the net phase change of each group of super units is π; Adjusting the height difference of the substrate surfaces corresponding to adjacent metacells to perform π phase compensation so that the single-medium metasurface covers a phase range of 0 to 2π; Based on the acquired phase gradient data sets at different deflection angles, the widths of the cellular structures of a group of superunits at different positions, and the height differences of the substrate surfaces corresponding to adjacent superunits, a single-medium metasurface with geometrically compensated phase is prepared using semiconductor micro-nano processing methods.

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